As evidenced by a large number of patents issuing recently, the coating of glass containers with plastic is becoming increasingly more prevalent. These coatings are applied for a wide variety of reasons, including protection of the pristine strength of the glass, prevention of the scattering of glass shards on shattering etc. In many of the prior art patents, this plastic coating is applied as a sheath which is wrapped about or shrunk onto the glass container. However, frequently, the best method of applying the plastic coating to the bottle involves some process other than application of a sheath or wrap of, essentially, precured plastic.
In the copending application, previously referred to, a method for application of an uncured plastic to a glass container is described. In accordance with this method, as set forth in that application, the plastic is applied while the container is attached to one work holder, while that coating is cured while the container is attached to a different work holder. The purpose is to prevent fouling of the first work holder with cured plastic. While the process described in that application is entirely adequate, and solves a real problem relating to the application of plastic coatings to glass containers, it does not deal with the specific treatment of the coated glass container after it is transferred from the first to the second work holder.
In general, the most efficient method and apparatus for curing of the plastic coated glass container is a heated oven where a plurality of coated glass containers may be passed through the oven in successive ranks. Employing such a method and apparatus, the coating on a plurality of glass containers are simultaneously, and gradually brought to a complete cure. The most effective method for conveying the coated glass containers through a curing oven, of the type referred to, is on a continuous, moving belt upon which the coated glass containers rest. However, if the containers are directly transferred from the first work holder of previously referenced application Ser. No. 415,972, to the second work holder, which, in this case, would consist of the continuous, moving belt, then curing of the plastic coating in the oven would include curing of the plastic coating on the bottom of the container to the continuous moving belt. In such a situation, either the coating on the bottom of the glass container would not be fully cured, or the cure would be such as to effectively bond the glass container to the continuous moving belt, so that removal of the container from the belt would involve damage to the coating, thus effectively defeating the purpose of the coating.
As previously indicated, in general, the most efficient method and apparatus for curing the plastic coating onto the glass container is by continuously moving it through an oven. While means exist for curing of such a plastic coating outside of a continuous oven, they are inefficient, and, in general, require inordinate amount of space and energy.
Accordingly, it is desirable to provide a method to allow for effective curing of a plastic coating on a glass container so that it can be completely cured in a continuous oven.